In a two-way radio communication system, handheld two-way radios and/or vehicular two-way radios communicate with each other in “direct mode” in which simplex transmissions between two devices are carried out directly over a shared channel. Because the communication system carries many communications at one time, a radio may need to monitor other communications in the system. Scan is a feature that allows a radio to monitor other communications in the system. During a scan, the radio locks on to a specific RF carrier signal and inspects activity that may be present on the carrier signal. A priority scan involves scanning a higher priority channel whilst engaged in actively (for example, a voice call) on a lower priority channel. The scan aims to determine whether any activity on the scanned channel is of interest, for example, whether the call on a scanned channel is addressed to the scanning radio. The scan involves switching away from the home-channel (RF) carrier signal of the active or in-use channel) on which the radio may be receiving a call, and switching to the RF carrier signal of the scan channel. This time away from the call during which the radio is engaged in on the active channel results in the radio missing some of the active channel call resulting in an “audio hole”. If the scanned channel is carrying a communication that is not addressed to the radio or the scanned channel has no communications at all, then the radio returns to the call that it was previously engaged in and listening to on the active/home-channel.
Scanning of channels may result in audio artifacts creating pop-like sounds which are annoying to the user of the radio. A trivial solution to mask the pops is to mute the speaker for an extended duration so that the pops die down. However, this increases the time during which home-channel audio is masked out which is undesirable to the user of the radio. Various approaches for minimizing audio holes have included digital frame repetition in which a vocoder frame is repeated during priority sampling time that masks the audio hole. However, this approach can not be used in analog transmissions. Audio reconstruction approaches to minimizing audio holes involves linear predictions schemes. However, the performance of the audio reconstruction approaches is limited by signal-to-noise ratio as well as the types of speech/audio signals being processed. Channel marking approaches use past activity on a priority channel to adjust the priority sampling time (for future scans) and the sampling rate (how often to scan). However, the channel marking approaches use apriori information to alter the priority channel list and do not address minimizing the actual audio hole.
Accordingly, there is need for an improved priority channel scan for audio hole suppression in two-way radios.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.